1. Field of the Invention
This invention relates to applications where software code is being developed for a read only memory (ROM) device inside a system which will need to run the ROM code and code from an external memory simultaneously. An important example of this type of application is a digital signal processing device software development application.
2. Description of the Prior Art
Often, when developing ROM code for an application, a developer will want to test the code before implementing it on a chip inside of ROM, because that implementation can be expensive and time consuming. In the prior art, a solution has been to use the external bus interface to external memory for this purpose. The code to be tested is placed in the external memory. Once it is there, it can be accessed by the external bus interface, and therefore by the elements of the system that can access the external bus interface. The code, then, does not need to be resident in the ROM to be tested; placing the code in external memory provides all the access to the code that is needed for testing.
A problem occurs, however, when attempting the testing of applications which, when operational, will require access to the external memory. Trying to test them according to the methods disclosed in the prior art will clearly not work - the external memory must be left alone to be used by the application and at the same time would be needed for storing the code to be tested. The instant invention works to solve this problem without forcing the software developer to create a ROM chip for each version of the code that must be tested which is costly and time-consuming.